Characterization of a new type of phosphopantetheinyl transferase for fatty acid and siderophore synthesis in Pseudomonas aeruginosa.

Phosphopantetheinyl-dependent carrier proteins are part of fatty-acid synthases (primary metabolism), polyketide synthases, and non-ribosomal peptide synthetases (secondary metabolism). For these proteins to become functionally active, they need to be primed with the 4'-phosphopantetheine moiety of coenzyme A by a dedicated phosphopantetheine transferase (PPTase). Most organisms that employ more than one phosphopantetheinyl-dependent pathway also have more than one PPTase.

The nuclear export receptor Xpo1p forms distinct complexes with NES transport substrates and the yeast Ran binding protein 1 (Yrb1p).

Xpo1p (Crm1p) is the nuclear export receptor for proteins containing a leucine-rich nuclear export signal (NES). Xpo1p, the NES-containing protein, and GTP-bound Ran form a complex in the nucleus that translocates across the nuclear pore. We have identified Yrb1p as the major Xpo1p-binding protein in Saccharomyces cerevisiae extracts in the presence of GTP-bound Gsp1p (yeast Ran).

Nup2p, a yeast nucleoporin, functions in bidirectional transport of importin alpha.

Import of proteins containing a classical nuclear localization signal (NLS) into the nucleus is mediated by importin alpha and importin beta. Srp1p, the Saccharomyces cerevisiae homologue of importin alpha, returns from the nucleus in a complex with its export factor Cse1p and with Gsp1p (yeast Ran) in its GTP-bound state. We studied the role of the nucleoporin Nup2p in the transport cycle of Srp1p.

Assembly of heterodimeric luciferase after de novo synthesis of subunits in rabbit reticulocyte lysate involves hsc70 and hsp40 at a post-translational stage.

Heterodimeric luciferase from Vibrio harveyi had been established as a unique model enzyme for direct measurements of the effects of molecular chaperones and folding catalysts on protein folding and subunit assembly after de novo synthesis of subunits in rabbit reticulocyte lysate. It was observed that luciferase assembly can be separated in time from synthesis of the two subunits and that under these post-translational conditions assembly was inhibited by either ATP depletion or inhibition of peptidylprolyl cis/trans isomerases, that is, by addition of cyclosporin A or FK506. Furthermore, it was observed that the inhibitory effect of FK506 on luciferase assembly can be suppressed by addition of purified cyclophilin, thereby providing the first direct evidence for the involvement of peptidylprolyl cis/trans isomerases in protein biogenesis in the eukaryotic cytosol.